Greetings Alan,
We have just replaced the seats in our three piece suite at home with the foam you mention from Tockfield.
I took note of their advice regarding the weights of the user.
Now I'm 15st plus a bit so we plumped for the medium 600.
If I were to be brutally honest, the seats are a little firm for my taste but a million times better than what it replaced (A three year old M and S suite that has hardly had any use whatsoever. Anybody from M and S out there. Please note)
However, I would feel comfortable if I were to sleep on it (I like a firm mattress.) so it really is a matter of taste.
The Chief Fairy is overjoyed with the difference but a little put out at the thought that she will now have to wait for a replacement three piece suite.
If there is any chance of you visiting the factory I would take up the opportunity because once bought you are stuck with it.
Any questions, don't hesitate.
Regards